Various physiological effects of lactic acid bacteria, such as intestinal regulation effect, defense against infection, immunostimulatory action, and cancer prevention, have been found one after another, and developments have been made for using lactic acid bacteria or cultures thereof as materials for health foods, drugs, or the like. Moreover, recent studies have reported that the above-mentioned functions can be improved by delivering the lactic acid bacteria in a viable condition to intestines, and improvement of the viability in the product has a great industrial advantage in applications to Foods for Specified Health Use (FOSHU) rapidly increasing the demand for the foods in recent years.
However, the viability of a lactic acid bacterium is affected depending on the bacterial strain, culture phase, product pH, or concentration of sugar used as a sweetener, and it is very difficult to improve the viability of the lactic acid bacterium while keeping the original taste of the product. Therefore, special containers are used in order to suppress oxygen permeation as much as possible, but the containers have a problem of increase in the cost. Moreover, as a method of producing a low-fat yogurt causing little decrease in a lactic acid bacterium during storage, a method of improving the survival rate of the lactic acid bacterium by adding oleic acid, or a salt or ester thereof to a fermentation medium has been disclosed (for example, see Patent Document 1). However, most of oleic acid-related compounds that may be used as food additives in Japan have distinctive smells, and use of the compounds inevitably results in deterioration of the flavor of the products. Even though the viability is improved while deteriorating the flavor, the survival rate is as low as 40%.
Furthermore, a method of producing a liquid yogurt with low viscosity and high viability by adding peroxidase to a raw material mixture has been disclosed (for example, see Patent Document 2), but there is a problem that addition of such material may affect the cost of the product.
On the other hand, in order to exert physiological effects of a lactic acid bacterium, it is important to maintain a larger number of viable cells in the product. However, to increase the number of viable cells, it is necessary to take longer culture time, resulting in deterioration of productivity. A method of promoting the growth of lactic acid bacteria to increase the bacterial cell concentration and to shorten the culture time enables simple and inexpensive production of a culture of lactic acid bacteria and is highly significant from the industrial viewpoint.
Various attempts have been made as methods of promoting growth of lactic acid bacteria. For example, there have been disclosed Euglena cell and/or an extract thereof (for example, see Patent Document 3), a product obtained by removing high-molecular materials from a cucumber extract (for example, see Patent Document 4), a degradation product obtained by treating whey protein with protease (for example, see Patent Document 5), sake lees (for example, see Patent Document 6), a purified pyroligneous acid solution (for example, see Patent Document 7) and the like. Addition of such substances may affect the flavor of the product and raise a problem of an increase in the cost due to complex and cumbersome processes in preparation or purification of the materials.    Patent Document 1: JP-A-2001-45968    Patent Document 2: JP-A-H10-262550    Patent Document 3: JP-A-H07-99967    Patent Document 4: JP-A-2000-41655    Patent Document 5: JP-A-2004-57047    Patent Document 6: JP-A-2005-151927    Patent Document 7: JP-A-2005-318856